Large off-highway trucks carry large quantities of ore or overburden over haul roads in open pit mines or in other applications. The conditions in which these trucks are used are typically severe. The haul roads may have ruts, potholes, or large rocks interspersed throughout the work site and must be negotiated by the off-highway trucks. Mine managers attempt to reduce the stresses applied to the trucks by regularly maintaining the haul roads. Many of the obstacles are dependent on the location of the work site or weather conditions and cannot be completely eliminated.
Given the huge weights of materials being hauled, these obstacles can cause the frame of a truck going over the obstacles to twist. These twisting moments cause the truck structural components to fail over time due to metal and weld fatigue. The more severe the work environment, the shorter is the expected fatigue life of the structural components.
Load imbalances may also contribute to fatigue failure by causing similar twisting actions of the truck frame and other structural components. Load imbalances can cause further damage during dumping of the material since the weight is concentrated on the rear of the truck frame when the dump body is raised. The problems associated with truck overloading and load imbalance is therefore exacerbated during dumping.
These trucks represent huge investments and cause great losses of productivity if they require maintenance at unscheduled times. Certainly, one of the most critical aspects in the performance of complex machines such as mining trucks is the structural integrity (e.g., fatigue life) of the major load carrying elements such as the main frame, dump body, and the suspension undercarriage components. It is therefore critical for proper work site management to understand when a truck is being used such that expected life is being reduced. Actions can then be taken to correct whatever is causing the reduction in expected fatigue life of the structural components.
Prior systems have relied upon experience and rough approximations to predict frame life and roading or loading conditions that may cause frame damage. This practice introduces considerable subjectivity into the system and results in the vehicle being operated abusively without knowledge of the extent of potential damage or the causes of damage. It is a somewhat daunting task for a structural design engineer or structural analyst to predict with high confidence the life of such complex structures when they are operated in a wide variety of environments.
Knowledge of potentially damaging events would be useful to not only work site managers, but also the driver of the truck and the operator of the machine loading the truck. For example, the driver could slow the truck down before reaching a particular part of the haul road if during the previous trip he went over a bump and was notified that this caused an event contributing to a shortened frame life. Similarly, if the operator of the machine loading the truck is notified that the load is imbalanced, then he can strive to improve balance by placement of subsequent loads. Furthermore, mine management can use such data to recognize operator abuse of the truck and to improve maintenance of the haul roads. For example, if the mine manager recognizes that the number of potentially frame damaging events is increasing, he can infer that haul road quality is decreasing so that maintenance should be increased.
Other systems, such as the one disclosed in U.S. Pat. No. 4,635,739 issued to D. Foley et al. on Jan. 3, 1987, have shown that strut pressure can be an accurate indicator of payload. The apparatus disclosed therein includes an electronic control that monitors each of the strut pressures, compensates for various inaccuracies introduced by load distribution and vehicle attitude, and correlates this information into actual payload. This payload information allows the truck to be operated efficiently near its maximum capacity without promoting undue vehicle wear. An overloaded vehicle hastens tire and frame damage.
While systems of this type provide accurate indications of payload, they are incapable of identifying events that are sufficiently severe to contribute to frame damage. Payload monitors can provide indications that the load in the truck is above or below its rated capacity; however, frame damage depends upon many other factors and is caused primarily by situations involving uneven stresses rather than simply overloading the truck. Even though a truck is loaded below capacity, it can still undergo events contributing to frame failure. Such damage typically occurs by such events as hitting potholes or ruts or dumping an unbalanced load.
No system available in the prior art correlates suspension and/or load characteristics to the estimated life of the frame. The frame of vehicles of this type are typically complex welded structures and frame damage cannot be correlated directly to payload alone. Due to the complexity of the frame, damage can occur in any of a variety of areas and different types of events can cause damage to different areas. Prior art systems have also not accumulated frame stress data to indicate trends in work severity.
The present invention is directed to overcoming one or more of the problems as set forth above.